In a distillation column where at least one of the feed streams contains a gas/liquid mixture, with a large fraction of the gas produced by a vaporization means upstream of the distillation column, it is necessary that the gas be directed to a separation section above the feed stream location. Usually it is desirable to separate the liquid from the gas more or less completely. Additionally, it is desirable to change the flow direction of the gas portion of the mixture. Most often the flow direction of the gas phase needs to be changed from a horizontal flow into a vertical or upward flow. The separation section which receives the gas flow also operates best when the gas is distributed uniformly across the entire cross-sectional area of the separation section.
In gas/liquid mixture contacting devices operating under vacuum pressure, the mixture entering the contacting device often has a high velocity. This high velocity makes any abrupt changes in the direction of flow difficult. Non-ideal distribution of the gas portion of the mixture to the cross section above the feed stream location correlates to the gas flow having high local vertical velocity component peaks when entering the contacting section.
The high velocity of these streams creates challenges to the design of gas/liquid contacting devices. The vertical distance between the feed inlets and the separation section above it should be kept minimum in order to keep the manufacturing cost of the contacting device reasonable. Additionally, increased contacting device height at this point/part also creates extra cost for auxiliary equipment such as pumps, as they have to be designed for increased capacity parameters (such as pump head). Further cost items impacted by increased contacting device height include structural steel, cabling, foundations etc.
One area in which gas/liquid contacting devices where the above described conditions prevail are in oil refineries; specifically in the atmospheric crude distillation unit, in the vacuum distillation unit for atmospheric crude bottoms and in various other distillation columns. A specific location in other distillation services is the reboiler return arrangement to the column, where the gas/liquid mixture is introduced to the column from a reboiler, often as flashing feed, which serves as vaporization means.
One of ordinary skill in the art will recognize that the above described conditions are present to at least some degree in all contacting devices where a feed is introduced to the device.
WO 2007/089888 and U.S. Pat. No. 5,972,171 address a separate problem of entrainment, a condition where rising vapor from a feed entrains impurities or contaminants, by altering the location and arrangement of feed inlets. In addition to this they introduce de-entrainment devices in the area of a feed inlet which consist of one or more plates in series, arranged in a radial fashion similar to that of a stopped fan and having a conduit located in the center of the radial plates. The purpose of these devices, unlike that of the present invention, is for the plates to be arranged substantially planar to the feed inlet so that the feed flows along the surface of the plate to produce a more pure vapor stream.
The present invention improves upon the prior art for at least the reasons that the feed distribution device, by itself, creates a resultant feed flow distribution within the input column section which does not require the feed inlets to be rearranged, creates a minimal pressure drop and is substantially simpler in design so that the feed flow dynamics of the system can be easily calculated and modeled.